1. Field of the Invention
The present invention relates to a rotary electric machine and, particularly, a generator-motor.
2. Description of the Related Art
A dc electric rotary machine has been used as a generator-motor for a long time. Because such a dc motor has brushes, the lifetime is limited. Although an ac rotary electric machine with a two-way power converter or an inverter has been used as the generator-motor recently, the inverter necessitates many power transistors of a large capacity to control a large amount of multi-phase current, resulting in an expensive motor-generator having a complicated structure.